1. Field of the Invention
The present invention relates to an ink jet printer, and more particularly to a head unit detachably mounted on an ink jet printer body.
2. Description of the Related Art
Ink jet printers have been known and extensively used in the art. Typically, a head unit is detachably mounted on an ink jet printer body. The head unit includes a plurality of ink chambers and a plurality of nozzles in fluid communication with respective ones of the plurality of ink chambers.
U.S. Pat. No. 4,380,770 to Maruyama discloses an ink jet printer including pumped-forced circulation of ink through the printer head and a nozzle cap which together eliminate gas from the ink supply and overcome ink stagnation which adversely affect printing quality.
Because the ink chamber and the nozzle are of a fine structure, forced circulation is insufficient to eliminate fine bubbles once they are introduced into the ink chamber and generated in the ink circulation pathway.
The present invention has been made to solve the aforementioned problems, and accordingly it is an object of the invention to provide a head unit and an ink jet printer on which the head unit is mounted, wherein occurrence of defective printing due to air bubbles mixed with ink can be prevented.
To achieve the above and other objects, there is provided a head unit detachably mounted on an ink jet printer body. The head unit includes an ink head formed with a plurality of ink chambers and a plurality of nozzles. The nozzles are fluidly connected to respective ones of the ink chambers individually. The head unit further includes a manifold, a buffer tank, and an ink supply channel. The manifold is fluidly connected to the plurality of ink chambers so that ink is supplied from the manifold to the plurality of ink chambers. The buffer tank is defined by a ceiling wall, side walls, and a bottom wall. The ink supply channel is fluidly connected between the buffer tank and the manifold. Ink stored in the buffer tank is supplied to the manifold and the ink in the manifold is in turn supplied to the plurality of ink chambers for allowing ink droplets to be ejected from the plurality of nozzles.
The manifold is positioned below the buffer tank and the ink head is positioned below the manifold when the head unit is disposed in an orientation in which the head unit is intended to be used.
The bottom wall of the buffer tank is formed with a first aperture The manifold has an upper surface formed with a second aperture. The ink supply channel is provided between the first aperture and the second aperture. In the ink supply channel, a filter is disposed.
The inner surface of the ceiling wall is formed with a curved surface or with a slanted surface that intersects an imaginary horizontally extending plane. So the inner surface of the ceiling wall has an uppermost portion in which an outflow port is formed for removing air and ink mixed with bubbles from the buffer tank.
An ink introduction port is formed in the buffer tank for introducing ink into the buffer tank. The ink introduction port is disposed near to the inner surface of the bottom wall. The ink introduction port is made from a hollow tubular wall, which is formed in the ceiling wall to protrude downward into the buffer tank.
The ink jet printer body is provided with an ink circulation pathway. The buffer tank provided in the head unit is brought into a fluid communication with the ink circulation pathway when the head unit is mounted on the ink jet printer body.
An ink introduction port is formed in the buffer tank for introducing ink into the buffer tank. An introduction tube is fluidly connected to the ink introduction port for introducing ink into the ink introduction port. An introduction joint is provided which has one end fluidly connected to the introduction tube and another end fluidly connected to the ink circulation pathway provided in the ink jet printer body. Ink supplied from the ink circulation pathway is introduced into the introduction tube via the introduction joint. An outflow port is formed in the buffer tank, and an outflow tube is fluidly connected to the outflow port for removing air and ink mixed with bubbles from the buffer tank. An outflow joint is provided which has one end fluidly connected to the outflow tube and another end fluidly connected to the ink circulation pathway provided in the ink jet printer body. The air and ink mixed with bubbles are fed back into the ink circulation pathway via the outflow joint. Another end of the introduction joint is brought into connection with the ink circulation pathway, and another end of the outflow joint is brought into connection with the ink circulation pathway when the head unit is mounted on the ink jet printer body. On the other hand, another end of the introduction joint is disconnected from the ink circulation pathway, and another end of the outflow joint is disconnected from the ink circulation pathway when the head unit is detached from the ink jet printer body.
The introduction joint and the outflow joint have openings facing the ink jet printer body. The openings configure an imaginary plane that intersects an imaginary horizontal plane. Preferably, a casing is disposed below the openings of the introduction joint and the outflow joint to receive dripping ink.
The ink jet printer body includes an ink cartridge detachably mounted on the ink jet printer body, a sub-tank supplied ink from the ink cartridge, an ink supply pump, and a buffer purge pump. A first ink channel supplies the ink of the sub-tank to the buffer tank provided in the head unit. A second ink channel feeds back the ink stored in the buffer tank to the sub-tank. The buffer purge pump is disposed in the second ink channel to generate a flow of ink from the buffer tank to the ink supply source when driven and to interrupt the flow of ink when stopped. The buffer purge pump is stopped when ink droplets are ejected from any one of the plurality of nozzles. The third ink channel fluidly connects the ink cartridge with the sub-tank. The ink supply pump is disposed in the third ink channel to generate a flow of ink from the ink cartridge to the sub-tank when driven and interrupt the flow of ink when stopped.
A joint is provided which has a first inlet, a second inlet and an outlet. The third ink channel is divided into a first part and a second part, and the first part is connected at one end to the ink cartridge and another end to the first inlet. The second part is connected at one end to the outlet and another end to the sub-tank. The second ink channel is divided into a first part and a second part, and the first part of the second ink channel is connected at one end to the buffer tank and another end to the second inlet. The second part of the first ink channel is commonly used as the second part of the second ink channel.
A suction cap is further provided, which is movable toward the ink head to hermetically seal the plurality of nozzles. A suction pump is connected to the suction cap to suck ink in the plurality of ink chambers through the suction cap. The buffer purge pump interrupts the flow of ink when the suction pump is sucking ink in the plurality of ink chambers through the suction cap.